Can someone else explain to me what launchers are? Are they like themes for android? I did a search for 3d launchers and came across spb. It mentions phones so i assume that is what it is for. Is there a generally accepted best launcher for tablets ans one that is 3d?

I like Holo Launcher HD if I'm not using stock/Trebuchet. It has just enough customizations to make me happy while keeping a clean simple look. They are simple enough to install and try though, so a bunch of them and see what you like most. I don't know which ones are good for tablet though because I still don't have an Android tablet.

Seems like many of these launchers are meant for phones. How do I return to the default OS launcher once I've tried a bunch?

Settings -> Apps, find the one you have set as default currently and tap on it. If you scroll down a little on the info page for that app, you'll find a Clear Defaults button. Use that to remove the default launcher, then press home and select a new launcher to use.

There are also apps, I believe one was called Home Switcher, that accomplish the same thing.